1. Field of the Invention
The present invention relates to a semiconductor device and a field-effect transistor.
2. Background Art
Nitride compound semiconductors have high dielectric breakdown field strength, high heat resistance, and high electron saturation drift velocity, and hence can be used to provide electronic devices capable of high temperature operation and high power operation, as compared to Si-based or GaAs-based devices.
Incidentally, manufacture of a field-effect transistor, a type of electronic device, requires forming a gate electrode that has a Schottky characteristic with respect to the nitride compound semiconductor.
It has been reported that a Schottky electrode made of Ni (nickel), Pd (palladium), Pt (platinum), etc. having a large work function can be used with an n-type nitride compound semiconductor to achieve good electrical characteristics. However, since these metals do not have a very high melting point, the electrode degrades during high temperature or high power operation which electronic devices employing a nitride compound semiconductor characteristically perform.
To address the above problems, a method is proposed for using metal nitride for an electrode (see, e.g., Japanese Patent Laid-Open No. 2000-196109).
The above publication discloses that materials such as WN and TiN have a Schottky characteristic. However, this publication does not clearly show a principle, a crystal structure of material, and a composition ratio, a ratio of nitrogen to metal, for achieving a good Schottky characteristic. Therefore, the above method fails to produce satisfactory results.